The present invention relates to a method and a device for fixing fibrous pieces of material made of porous and springy material at a given distance from one another on one or more continuously advanced material webs and, for joining together, establishing an optional pattern on the piece of material, preferably for production of a material laminate for use in absorbent products. The absorbent products can consist of nappies, baby pants, incontinence pads, sanitary towels, panty liners or the like. The invention can also be used within other areas in which one or more shorter pieces of material are to be fixed on one or more continuous webs.
It is previously known to fix pieces of material on a web by gluing. The gluing procedure has been found to have considerable disadvantages such as, for example, the handling of additional material which also involves undesirable costs. Other disadvantages in the process using glue are that glue residues are deposited in inappropriate places in the equipment and thus create problems, and also that the use of glue involves extra cost, and glue layers in a liquid-transporting material laminate impair the prerequisites for liquid flow.
It is also known to join one or more continuous webs together by means of ultrasound. This is disclosed in, for example, WO 97/23340 which describes the use of ultrasonic horns in combination with rotating stays for joining continuous webs together in a given pattern, where the purpose of the pattern is to make possible intermittent joining together of two or more continuous webs. This known arrangement is not suitable for fixing short pieces of material to a continuous web.
The object of the invention and its most important characteristics.
The object of the invention is to solve the problems associated with the techniques indicated above and to make it possible to use ultrasonic welding for fixing pieces of material on a continuous web. Above all, the invention makes possible rapid, cost-saving and simple adjustments for adaptation to changed circumstances, for example a change of material or the exchange of various parts of the equipment, and adjustments in the event of patterns being exchanged. Moreover, the invention results in short operational stoppages for service and maintenance.
According to the invention, this is achieved on the one hand by a method in which each piece of material is attached to the continuous web by means of ultrasound in a first station, after which the piece of material is fixed by its entire contact surface by means of ultrasound in a second station, and on the other hand by a device consisting of a first station for attaching the piece of material to the continuous web and a second station in which the piece of material is fixed over its entire surface to the continuous web.
The invention results in the advantages that the material can be produced without the use of glue and thus the costs and service requirements are reduced.
The invention also affords the advantage that, by means of continuous energy supply to ultrasonic horns, pieces of material are fixed to a continuous web and at the same time a pattern as described in, for example, Patent Application SE 9801038-2 is obtained.